1. Field of the Invention
The present invention relates to a substrate for a monochrome liquid crystal display apparatus used for a monochrome liquid crystal display apparatus. More specifically, it relates to a substrate for a monochrome liquid crystal display apparatus capable of preventing deterioration of the display characteristics, and a production method therefor.
2. Description of the Related Art
Conventionally, a liquid crystal display apparatus has been used as the information displaying means in many fields, regardless of the monochrome type and the color type.
For example, the monochrome liquid crystal display apparatus has a structure comprising at least a substrate for a monochrome liquid crystal display apparatus having a substrate, a black matrix formed in a pattern on the substrate, and a protection layer provided for protecting the black matrix and ensuring the flatness of the substrate surface, a counter substrate facing the substrate for a monochrome liquid crystal display apparatus, and a liquid crystal layer clamped between the substrate for a monochrome liquid crystal display apparatus and the counter substrate.
Recently, as the gapping material (spacer) for constantly maintaining the gap between the substrate for a liquid crystal display apparatus and the counter substrate, a columnar spacer is used instead of the plastic beads, which have been used conventionally. That is, in order to solve the problems of the contrast deterioration derived from the light leakage in the vicinity of the plastic beads and the display irregularity derived from the distribution irregularity, a columnar spacer is formed on the side of either substrate, and the gap between the two substrates is maintained constantly by the spacer.
For example, Japanese Patent Application Laid Open (JP-A) No. 11-109366 discloses a technique using a columnar spacer comprising a large diameter spacer comprising one layer and a small diameter spacer comprising two or more layers for preventing generation of the irregularity in terms of the height of the columnar spacer itself in the liquid crystal display apparatus display area and the outside of the display area. Furthermore, JP-A No. 2002-148426 discloses a technique for constantly maintaining the shape of the columnar spacer according to the two layer structure of a columnar spacer comprising a low deformation part with a small deformation amount in the high temperature and high pressure, and a high elasticity part capable of following the contraction of the liquid crystal at a low temperature for preventing the change of the columnar spacer by the influence of the high temperature and high pressure at the time of assembling the liquid crystal display apparatus. Moreover, JP-A No. 11-2717 discloses a technique for constantly maintaining the gap between the two substrates by projecting a columnar spacer from a predetermined position in a range of 1 to 4 μm.
According to an example of the conventional substrate for a monochrome liquid crystal display using the columnar spacer, as shown in FIG. 3, a black matrix 2 is formed in a pattern across the pixels on the substrate 1 for a monochrome liquid crystal display apparatus. The black matrix 2 is formed with the width narrower in a part corresponding to the pixel parts A as the display area in order not to lower the aperture ratio of the display area. In contrast, the black matrix 2 formed in the outer peripheral part B outside the display area is formed with the width wider in order to effectively block the light from the light source such as a back light.
Furthermore, a protection layer 3 is formed for covering the surface of the black matrix 2 for protecting the members such as the black matrix 2, and for providing the flatness to the surface of the substrate 1 for a monochrome liquid crystal display apparatus. According to the protection layer 3, the film thickness difference is generated between the pixel part A and the outer peripheral part B. This is because the protection layer 3 can hardly be laminated on the upper surface of the black matrix 2 disposed on the pixel part A with the width formed narrower so that the film thickness of the laminated protection layer 3 tends to be thinner. In contrast, since the black matrix 2 provided in the outer peripheral part B is formed with a sufficient width, the film thickness of the protection layer 3 is made thicker than that of the pixel part A. In the case the columnar spacer 4 is formed on the protection layer 3, due to the above-mentioned film thickness difference of the protection layer 3 itself, as to the height from the surface of the substrate 1 for a monochrome liquid crystal display apparatus to the upper surface of the columnar spacer 4, it is higher in the outer peripheral part B than in the pixel part A.
The height difference appears as the gap difference between the substrates so that the difference in the gap area significantly influences the display characteristics particularly in the IPS type monochrome liquid crystal display apparatus. Moreover, in the case the counter substrate 5 is disposed on the substrate for a monochrome liquid crystal display layer via the columnar spacer 4, distortion is generated in the counter substrate 5. The distortion generates the trouble of the light leakage from the counter substrate 5 peripheral part so that the problem of the brightness in the periphery of the screen is generated.
In order to solve the problems in the conventional substrate for a monochrome liquid crystal display apparatus, although a method of forming columnar spacers individually on the pixel part and on the outer peripheral part at the time of forming the columnar spacers is considered, it has been difficult to precisely adjusting the height due to the influence at the time of forming the columnar spacers in some cases.